In order to understand the mechanism(s) responsible for compartmentalization or acid hydrolases into lysosomes we are isolating and analyzing mutant CHO cells defective in this process. An initial step in compartmentalization involves interaction of the mannose 6-phosphate receptor with phosphorylated oligosaccharides on the hydrolases. We have examined the effects of several glycosylation defects on the ability of the oligosaccharide to serve as an acceptor of phosphate.